A 21-year-old woman developed severe starvation ketosis after self-administering tirzepatide obtained through online services, with serum 3-hydroxybutyrate reaching 2057 µmol/L. Starting at a normal BMI of 17.9, she dropped to 15.6 after two months of unsupervised use, requiring emergency hospitalization for bilious vomiting and presyncope. The case subsequently led to her diagnosis with anorexia nervosa, binge-eating/purging type. This represents a critical intersection of two concerning healthcare trends: the proliferation of online GLP-1 prescribing services and the rising prevalence of eating disorders among young adults. The dual GIP/GLP-1 receptor agonist's potent appetite suppression effects, while beneficial for appropriate candidates, can become dangerous in individuals with underlying eating disorder vulnerability. The case exposes significant gaps in online medical oversight, where brief virtual consultations may miss psychiatric red flags or body dysmorphia. With tirzepatide and similar drugs increasingly accessible through telehealth platforms, healthcare systems must develop better screening protocols to identify at-risk individuals. The persistent elevation of ketones months after metabolic stabilization suggests that biochemical recovery lags behind clinical improvement, indicating the need for extended metabolic monitoring in such cases.